Gas turbine tail burner fuel control



Feb, 28, 1950 w. s. BOBIER, JR 2,498,939

GAS TURBINE TAIL BURNER FUEL CONTROL Filed Nov. 1, 1948 GOVERNOR 1 1419. B05 is 1 Jr.

INVENTOR.

Patented eb. 28, 1950 GAS TURBINE TAIL BURNER FUEL CON Wilfred S. Bobicr, Jr., Grosse Pointe Woods, Mich., assignor to George M. Holley and Earl Holley Application November 1, 1948, Serial No. 57,654

11 Claims. (Cl. 60-355) The object of this invention is to supplement the power developed by a gas turbine in an ordinary airplane installation (jet propulsion) with "After Burning" (tail burner).

The figure shows the preferred form of my invention.

In the figure, I is the compressor delivering compressed air to the burner i2 which drives the compressor it through the gas turbine l I. i4 is the After Burning" burner (tail burner). 06 is the control of the area of the tail outlet and i1 is the second stage combustion chamber. i is the spark plug therein to ignite the tail burner l4. i8 is the main fuel pump for the gas turbine fuel. 2|) is the speed governor for the gas tarbine, both driven by the gas turbine H. 2| is the manual control for selecting the speed. 22 is a venturi in the fuel outlet leading to the main burner i2 of the gas turbine 24 and 26 are two passages, 24 at the high pressure and 26 at the lower pressure in the throat of the venturi 22, leading to the opposite side of the moving wall (diaphragm) 28. Moving wall 28 moves down in response to high fuel flow through venturi 22 and closes After Burner" control valve 33. Valve 3!) moves with wall 28 and admits more or less fuel to the nozzle l4 through the passage 56. The pressure difference acting on the wall 24 is increased at high altitude by valve "and decreased at sea level when valve 41 opens into the position shown. If the burner l4 blows out then the pressure in chamber l'l, downstream from gas turbine l I drops and the turbine speeds up and governor 20 cuts down main fuel through venturi 22. Micro-switch 43 then closes and the electrical circuit is completed and the spark plug I6 is reactivated by the battery l3 and the coil 9|. A diaphragm SI and a spring 53 are adjusted so that normally the fuel flow through venturi 22 opens the micro-switch 49.

A second moving wall (diaphragm) 32 opposes the motion of the first moving wall (diaphragm) 28; the centrifugally responsive weight 40 moves out as the engine speeds up and establishes a pressure difference to balance said centrifugal force. The higher the speed the lower the pressure in the passage 36. This higher speed pro duced a pressure difference acting on the moving wall 32 to open up the flow of fuel past valve 30 to the After Burning" burner i4. The manually adjusted temperature control 66 and the automatic temperature control 64 reduce the pressure difference between the two sides of moving wall 32 as temperature rises so as to reduce after-burning at high atmospheric temperature.

Automatic temperature responsive device may preferably be located in an air stream from passage 23, which passage has an entrance located in the air entrance and directs air which flows around the altitude corrector 91, inside the chamber 36, and temperature corrector 94, inside the chamber 33. Partially evacuated bellows 91 being more completely evacuated than the bellows 34. There is a restricted outlet I23 from chamber 93.

The tail burner fuel pump 42 is driven by the gas turbine H and draws fuel from passage 62 and delivers fuel to fuel passage 56 via passage 44, past check valve 50, past automatic valve and shut oil valve 54 in passage 56.

The rate of flow across the valve 30 is determined by the position of the two movin walls 28 and Y32 and the pressure drop across the valve 36. A valve 51 and spring 58 maintain this pressure drop constant and return excess fuel to the passage 60 which returns this fuel to the pump 42.

Passage 46 delivers fuel under pressure to act on the outer left hand side of piston 40, inside rotating wheel 38. Passage 48 delivers lower pressure fuel to act on the right hand (inner) side of the piston 40 whereupon the cylindrical valve 4i, carried by the piston 40, admits fuel from passage 48 to passage 36. Actually pres-,

sure in passages 36 is intermediate between low pressure in passage 48 and high pressure in passage 46. A stabilizing spring I4! is added pushing the floating piston in the same direction that the pressure in passage 46 acts.

The essential element of my invention is the establishment of a balance between a pressure on diaphragm 32 responsive to revolutions per minute squared and the pressure responsive to the rate of fuel flow to the gas turbine squared acting on the diaphragm 28. When these two pressures are out of balance, the balance is restored by an automatic valve 30, controlled by both of these two pressures and controlling the flow of fuel to the afterburners I4. The amount of power output of the tail burner I4 is only A; of the power output of the gas turbine burners l2 per pound of fuel burnt per minute. Hence, the need for limiting the utilization of the afterburning.

Operation For the sake of clarity two assumptions are made-(1) i8 partly closed (2) l6 open.

(1) The tail burners l4 get no fuel at all because flow through 22 is sumcient to overcome the feeble force of the speed responsive force acting on the diaphragm l2 and valve 30 remains closed.

(2) Flow from the main gas turbine burners I! immediately drops because the restriction around it is less and the power to drive compressor III is diminished and it thus takes much less fuel to maintain the gas turbine speed selected by manually controlled lever 2!. When the force responsive to the flow through venturi 22 falls, the valve 30 opens and micro-switch 49 closes responding to diaphragm 5i and spring 53. The spark plug i5 is immediately reactivated. Igniting burner it raises pressure in tail burner compressor chamber i1 and speed tends to drop, hence, governor automatically increases flow through venturi 22 and the ignition is thus automatically disconnected.

What I claim is:

l. A gas turbine compressor unit having an air entrance and a first combustion chamber and a first burner therein located upstream from said gas turbine and downstream from said compressor, a second combustion chamber located adjacent to and downstream from said gas turbine, a second burner referred to as the tail burner therein, a variable outlet from the second combustion'chamber, a flow control valve located therein downstream from said second burner, a first fuel pump and a selectively controlled speed governor driven by said gas turbine and discharging a governed quantity of fuel to said first burner, a second fuel pump also driven by said gas turbine and having an outlet therefrom leading to said second burner, a fuel restriction in the outlet from said first fuel pump, a first fuel chamber, a first moving wall therein dividing said chamber into two parts, fuel passages connecting these two parts to the fuel outlet at said restriction so as to subject the first moving wall to the pressure drop at said restriction due to fiow of fuel therethrough, a second chamber, a second moving wall therein dividing said second chamber into two parts, turbine speed responsive means automatically adapted to create a pressure difference in the two parts of said chamber that varies with the square of the speed of the turbine, a tail burner control valve controlling the flow from said second fuel pump to said tail burner connected to both of said moving walls in such a way that the increase in the fuel fiow to the first burner closes and an increase in turbine speed opens said tail burner control valve.

2. A device as set forth in claim 1 in which.

there is a valve to maintain a constant drop in pressure at said tail burner fuel control valve.

3. A device as set forth in claim 1 in'which there is a chamber connected to the air entrance to the gas turbine so as to be at the atmospheric pressure existing therein, a pressure responsive element in said chamber, a bypass around said first moving wall, a valve therein connected to said pressure responsive element so as to reduce the pressure difference acting on said first moving wall at sea level.

. 4. A device as set forth in claim 1 in which there is a chamber connected to the air entrance to the gas turbine so as to be at the atmospheric temperature existing therein, a temperature responsive element in said chamber, a bypass around said second moving wall, a valve therein connected to said temperature responsive element so as to reduce the pressure difference acting on said second moving wall at high temperature.

5. A device'as set forth in claim 1 in which there is an ignition device in the second combustion chamber, electric activating means therefor, a switch controlling the electrical means, a third moving wall located in said first fuel chamber, yieldable means tending to close said switch, the pressure drop in said fuel restriction acting on said third moving wall so as to open said switch at high fuel flow through said fuel restriction.

6. A device as set forth in claim 1 in which there are means responsive to the pressure of the air in the air entrance to the gas turbine to reduce the fuel fiow to said tail burner at high altitudes and low air pressures.

7. A device as set forth in claim 1 in which there are means responsive to the temperature of the air in the air entrance to the gas turbine to reduce the fuel flow to said tail burner at high air temperatures.

8. A device as set forth in claim 1 in which there are spark ignition means in said second combustion chamber, electric activating means therefor, a switch controlling the electrical means, means responsive to the fuel flow to the first combustion chamber to open the switch at high fuel flow and to close the switch at low fuel flow.

9. A gas turbine air compressor power unit having a source of fluid fuel under pressure and an air entrance and an air compre sor therein driven by said gas turbine, a first combustion chamber downstream from said air compressor having a fuel entrance connected to said source,

said gas turbine being rotated by the gases from said first combustion engine, a second combustion chamber located downstream of said gas turbine, a fuel entrance cpnnected to said source and leading into said second combustion chamber, a fuel control for said first and second combustion chambers comprising manual means for regulating the fuel flow to the first combustion chamber and automatic means for controlling the flow to the second combustion chamber including first means responsive to an increase in fuel flow to first'combustion chamber, second means responsive to an increase in temperature of the air entering the air compressor, third means responsive to an increase in pressure of the'air entering the air compressor,'the fiow to the second combustion chamber being regulated inversely to the first, second and third means.

10. A fuel control device as set forth in claim 9 in which there are speed responsive means responsive to the speed of the turbine compressor tending to increase the fuel flow to said second combustion chamber at th high turbine compressor speeds.

11. A fuel control device as set forth in claim 9 in which there are fuel ignition means for said second combustion chamber, activating means therefor, automatic control means for said activating means responsive to the first and third means which open the second fuel control.

WILFRED S. BOBIER, JR.

No references cited. 

